The present invention relates to a variable geometry turbine. The preferred, but not exclusive, field of application of the invention is in superchargers of internal combustion engines, to which reference will be made in the following description in a non-limiting manner.
Turbines are known that comprise a spiral inlet channel surrounding the rotor of the turbine and a vaned annular nozzle interposed radially between the inlet channel and the rotor. Variable geometry turbines (VGT) are also known in which the vaned annular nozzle has a variable configuration so that flow parameters of the operating fluid from the inlet channel to the rotor can be varied. According to a known embodiment, the variable geometry nozzle comprises an annular control member moving axially to vary the throat section, i.e. the working flow section, of this nozzle. This annular control member may be formed, for instance, by a vane support ring from which the vanes extend axially and which can move axially between an open position in which the vanes are immersed in the flow and the throat section of the nozzle is maximum, and a closed position in which the ring partially or completely closes the throat section of the nozzle. During the forward movement of the ring, the vanes of the nozzle penetrate through appropriate slots in a housing provided in the turbine housing in a position facing this ring.
Variable geometry nozzles of the type described briefly above have a number of drawbacks.
First, the vanes necessarily have to have a xe2x80x9cstraightxe2x80x9d profile, i.e. constant in the axial direction, without any torsion or variation of pitch angle. If not, the axial movement of the vanes in the respective slots would be possible only by providing substantial play between the vanes and the slots, which would be detrimental to the efficiency of the nozzle.
In addition to the design limits discussed above, nozzles with straight vanes sliding in respective slots are subject to problems of seizing; in practice even small geometrical errors due to manufacturing tolerances or heat distortions during operation may cause the nozzle to seize.
The object of the present invention is to provide a turbine with a vaned nozzle provided with an axially moving control member which is free from the drawbacks connected with known turbines and described above.
This object is achieved by the present invention which relates to a variable geometry turbine comprising a housing, a rotor supported in a rotary manner in this housing, the housing defining an inlet channel for an operating fluid in the form of a spiral surrounding the rotor, and an annular vaned nozzle of variable geometry interposed radially between the channel and the rotor so as to control the flow of the operating fluid from the channel to the rotor, characterised in that the annular vaned nozzle of variable geometry comprises a first vaned ring and a second vaned ring facing one another, each of the vaned rings comprising an annular member and a plurality of vanes rigidly connected to the annular member and extending towards the annular member of the other vaned ring, the vanes being tapered substantially as wedges so that the two pluralities of vanes may penetrate one another, at least one of the vaned rings being axially mobile with respect to the other vaned ring in order to define a variable throat section between the vaned rings.